The present invention fits within the field of lidars. Remote sensing by laser or lidar (acronym for “light detection and ranging” or “laser detection and ranging”) is a remote measuring technique based on the analysis of the properties of a beam of light returned toward its sender.
In particular, lidar systems are used to determine the speed of aircraft relative to the atmosphere. In this case, a laser beam is sent in the direction in which the aircraft is moving. The backscattering of the laser beam on the particles present in the atmosphere, for example dust or water droplets, generates a signal detected by the lidar system. Using Doppler effect analysis, it is then possible to determine the speed of the aircraft relative to the particles, and therefore relative to the ambient air.
For example, lidar systems are said to be “single-particle” when the laser beam is focused at a short distance from the emitter, over an area with a small volume. Thus, at aircraft cruising altitudes, few particles are present at the same time in the area in which the beam is focused. Such systems have high measurement availability.
However, the use of a laser beam is not without risks. In particular, the light beam, coherent and with a small diameter, has a high power, which may reach a watt or more. Consequently, an object placed in the beam may be seriously damaged. In particular, an operator crossing the beam, for example when the aircraft is on the ground, risks experiencing burns, in particular ocular.
These risks limit the use of such systems when an aircraft is on or near the ground, since the laser beam must then be cut by the pilot to avoid any burn risk. Additional systems are therefore necessary to measure the ground speed.